As long as it is untreated, it's fine (if it's shiny and slick like the granite used for countertops, it should probably not be used).
Do you know where to buy some untreated granite cuz I only see the shiny one...
Not sure, I have never looked for it. I would think your best bet would probably be the outdoor section at Lowes or Home Depot.
sry i should have said tombstone makers just ask them if they have any bits its free, i got a few pices off them a few years ago i still have them i made a cave/bridge with 3 bits that wer about 4inx4in, well worth a scout around if ther is a place like that near you,